1. Field of the Invention
The present invention relates to a noise-prevention grommet used in an automobile. More particularly, the invention relates to a grommet fixed to a wiring harness and an automobile body panel which partitions an engine compartment and a passenger compartment. The grommet is positioned at the intersection of the harness and the body panel, such that it prevents water and dust penetration from the engine compartment to the passenger compartment. Moreover, it improves noise insulation.
2. Discussion of Background Information
As shown in FIG. 1, when a harness is wired through the body panel 4 which partitions the engine compartment X and the passenger compartment Y, a known grommet 3 is fixed on the body panel and shields the passenger compartment Y from water and dust.
As shown in FIG. 2, the known grommet 3, made of a rubber or an elastomer, is an integral piece having two portions. One is a small tube portion 1 to be fixed on the circular surface of the wiring harness. The other is a frustoconical tube portion 2 flaring therefrom.
Electrical cables W are first bundled, then a tape T1 is helically wound thereon to create the wiring harness. The harness is passed through the grommet 3 and is fixed by firmly winding a tape T2 around the small tube portion 1 from the outside. The frustoconical tube portion 2 is provided with a fitting recess 2a on the outer circular surface of its flared end portion, while the body panel 4 is provided with a through-hole 4a. When mounting grommet 3 and a wiring harness W/H to an automobile, the grommet 3 is passed through the hole 4a, such that the rim of hole 4a is fitted in recess 2a.
The installation of grommet 3 and harness W/H into hole 4a of body panel 4 can be done either from the passenger compartment or the engine compartment. In either case, it is necessary to deform the frustoconical tube portion 2 when passing grommet 3 through hole 4a. The frustoconical tube portion 2 thus has a thinly constructed flaring portion 2b.
Noise generated in the engine compartment X (shown by arrows in FIG. 2) is transmitted through a thinner portion of the frustoconical tube portion 2 towards the inside of the grommet 3. The transmitted noise (shown by dotted arrows) passes therefrom through a space S formed between the external surface of the harness and the internal surface of the grommet, then into the passenger compartment Y.
The problem of noise-shielding has not been taken into account in the known grommet, so that the passenger compartment is rendered somewhat less comfortable because of this noise diffusing through the path hole of the harness.
To reduce the noise in the passenger compartment, it is proposed to fill the space S beforehand with a rigid material 6, as shown in FIG. 3. However, this rigid material makes it difficult to pass the wiring harness through the grommet. Another possible method is to fill space S with a sealing agent. However, this method adds another working step, i.e., the step of filling with a sealing agent.
Moreover, according to the above methods, the rigid material 6 or the solidified sealing agents prevent the grommet from deflecting, so that positioning the body panel becomes difficult. In addition, the wiring harness W/H becomes less flexible in the region where it passes through the grommet, so that positioning the wiring harness in the car body becomes more difficult. Accordingly, in the past, attempts to reduce the transmitted noise led to decreased workability.